title: Intracellular signal triggered by cholera toxin in Saccharomyces boulardii and Saccharomyces cerevisiae.
abstract: As is the case for Saccharomyces boulardii, Saccharomyces cerevisiae W303 protects Fisher rats against cholera toxin (CT). The addition of glucose or dinitrophenol to cells of S. boulardii grown on a nonfermentable carbon source activated trehalase in a manner similar to that observed for S.cerevisiae. The addition of CT to the same cells also resulted in trehalase activation. Experiments performed separately on the A and B subunits of CT showed that both are necessary for activation. Similarly, the addition of CT but not of its separate subunits led to a cyclic AMP (cAMP) signal in both S. boulardii and S. cerevisiae. These data suggest that trehalase stimulation by CT probably occurred through the cAMP-mediated protein phosphorylation cascade. The requirement of CT subunit B for both the cAMP signal and trehalase activation indicates the presence of a specific receptor on the yeasts able to bind to the toxin, a situation similar to that observed for mammalian cells. This hypothesis was reinforced by experiments with 125I-labeled CT showing specific binding of the toxin to yeast cells. The adhesion of CT to a receptor on the yeast surface through the B subunit and internalization of the A subunit (necessary for the cAMP signal and trehalase activation) could be one more mechanism explaining protection against the toxin observed for rats treated with yeasts.
authors.affiliation: Laboratório de Fisologia e Bioquímica de Microorganismos, Escola de Farmácia, Universidade Federal de Ouro Preto, Brazil.
authors.forename: R L
authors.initials: RL
authors.lastname: Brandão
authors.forename: I M
authors.initials: IM
authors.lastname: Castro
authors.forename: E A
authors.initials: EA
authors.lastname: Bambirra
authors.forename: S C
authors.initials: SC
authors.lastname: Amaral
authors.forename: L G
authors.initials: LG
authors.lastname: Fietto
authors.forename: M J
authors.initials: MJ
authors.lastname: Tropia
authors.forename: M J
authors.initials: MJ
authors.lastname: Neves
authors.forename: R G
authors.initials: RG
authors.lastname: Dos Santos
authors.forename: N C
authors.initials: NC
authors.lastname: Gomes
authors.forename: J R
authors.initials: JR
authors.lastname: Nicoli
mesh_terms: D000818:Animals; D002772:Cholera Toxin / Q000378:metabolism / Q000494:pharmacology*; D000242:Cyclic AMP / Q000096:biosynthesis; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D012440:Saccharomyces / Q000187:drug effects / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000378:metabolism*; D014198:Trehalase / Q000378:metabolism
chemical_list: D002772:Cholera Toxin; D000242:Cyclic AMP; D014198:Trehalase